A ubiquitous information society, which provides optimal data services according to the state or environment of things, is now becoming a reality. The use of ubiquitous information processing devices using IC chips such as smart cards or radio frequency tags (RFID) is also becoming more widespread. Trials of these devices in applied services like electronic banking, physical distribution management, security management or information services are now under way.
In recent years, sensor network systems consisting of a sensor node, a base station and a business application server have been developed. The sensor node is attached to a man or an object, and is provided with a sensor which measures the state of the man or object. The business application server acquires information measured by the sensor node, and performs business application service procedures based on the acquired information. The base station relays communication between the sensor node and business application server.
A conventional radio tag transmits only individual identification information. On the other hand, sensor nodes can transmit the state of the man or object, so they are expected to find applications in advanced business application services.
A sensor node cannot perform its tasks independently, but needs to cooperate with a task program on the business application server. The business application server receives required information from many sensor nodes, and implements business application services based on the received information. The business application server must therefore process the information received from many sensor nodes efficiently.
Whenever the business application server of a conventional sensor network system measures each sensor node, it performs communication with the base station, database search, database storage and database commitment. Hence, if the number of sensor nodes to be measured increases, the data processing amount of the business application server will increase dramatically.
A sensor network system which reduces the data amount transmitted by the sensor node is known (e.g., JP-A No. 2004-32176). When transmitting plural numerical data, the sensor node in this sensor network system extracts master data therefrom. Next, the difference value of the extracted master data and each numerical data is calculated, and the calculated difference value is transmitted to the business application server. In this way, the data amount received by the business application server can be reduced.